The present invention concerns a spark ignited internal combustion engine operated with charge stratification having a main combustion chamber and an auxiliary combustion chamber, or "prechamber", connected to the main chamber by means of a short passage. The auxiliary combustion chamber is provided with a fuel delivery device as well as a device for igniting a combustable fuel-air mixture which is richer than the main combustion charge.
Spark ignited internal combustion engines of the type operated with stratified charges have been known for many years. Although many variants on this engine design have been developed, the basic idea of all stratified charge engines has been, through structural measures, to diversify the mixture composition of the cylinder charge, at the instant of ignition, in such a manner that an ignitable fuel-rich mixture is present in the immediate vicinity of the spark plug while the charge in the remaining combustion space is properly matched to the prevailing operating conditions of the engine. This latter combustion charge may therefore consist of a lean mixture or even of air.
While heretofore such engine designs have been aimed at ensuring the safe ignition of the cylinder charge, notwithstanding wide variations in the total mixture composition and/or permitting carburetor-fueled operation at higher compression ratios without reaching the knock limit, the stratified-charge method is viewed today primarily as a possible route to the reduction of noxious substances contained in the engine emissions.
In the known designs of internal combustion engines operated with mixture stratification, the combustion chamber is divided into a main combustion chamber, delimited by the piston, and an auxiliary or prechamber in communication with the main chamber. The prechamber is provided with an ignition device, such as a spark plug, and a fuel delivery device consisting either of a fuel injection nozzle or an intake valve for delivery of a fuel-rich mixture. The prechamber is connected with the main combustion chamber by a short passage so that, following ignition of the fuel-rich charge portion present in the prechamber, the flame front can advance into the main combustion chamber for the purpose of igniting of the main charge, which may be made much leaner than the charge in the prechamber in dependence upon the engine load.
Difficulties have been encountered in internal combustion engines of the above-described type, particularly when cold starting and during the warm-up phase. The fuel of the comparatively rich mixture present in the prechamber has a tendency to condense heavily on the cold chamber walls making it necessary, under these operating conditions, to supply an especially large quantity of fuel which can then be only imperfectly combusted.